Multi-omics study of microbe-host interactions in rosacea

Rosacea is characterized by inflammatory lesions that frequently show increased Demodex folliculorum density. Although rosacea shows a high prevalence and significantly affects the quality of life of patients, the underlying mechanisms, especially the role of cutaneous dysbiosis are largely unknown. Hence, we aimed to systematically characterize disease severity of rosacea patients in the context of mite density, the cutaneous microbiome and the host's transcriptome before and after 30 days of topical 1% ivermectin cream treatment. At day 30, a marked decrease in mite density was observed in 87.5% of patients. At day 0, distinct microbial community changes included the decrease in Cutibacterium acnes abundance, while Staphylococcus epidermidis colonization increased when compared to healthy volunteers. Interestingly, the insect symbiont Snodgrassella alvi was recovered from a highly Demodex-colonized patient and was eradicated alongside mites during treatment. Although topical ivermectin did not exert an effect on bacterial dysbiosis, the host's transcriptome significantly normalized and an “ivermectin transcriptomic signature” was defined. Findings of the present study support that rosacea lesions are associated with dysbiosis, however, improvement of clinical signs during topical ivermectin is not associated with normalization of the host's bacterial microbiome, but with the decrease of transcriptomic dysregulation as well as mite density.